In the automotive industry, engine friction and wear reduction by adding additives to an oil-based lubricant is one of the most appealing approaches for improving vehicle fuel economy. The potential benefits realizable from this technique can be readily applied to all vehicles at low cost. Additives have been added to oil-based lubricants to reduce friction and wear by creating chemical reactions between the additives and the metal surfaces. However, these chemical reactions are very slow and the reaction films thus formed are generally not uniform. It has also been proposed that metal surfaces may be coated with friction-reducing or wear-reducing films before they are assembled into a vehicle. However, the durability of these films is less than desirable and it is extremely difficult to repair damaged films after a vehicle has been assembled and operated.
The formation of wear-reducing films on metal surfaces immersed in aqueous solutions or molten slats by an electrochemical technique has been performed by others. Great difficulties were encountered when the same electrochemical technique was used in a process to form friction-reducing and wear-reducing films on metal surfaces immersed in oil-based lubricants. Since oil-based lubricants have extremely high electrical resistance, electrical current cannot pass through the lubricants.
In our previous U.S. Pat. No. 4,714,529 issued Dec. 22, 1987, an electrolytic additive of dialkyl hydrogen phosphate was added to an oil-based lubricant and iron phosphate films were formed on cast iron surfaces. However, the durability of these films formed was found to be inadequate in motor vehicle engine applications.
It is therefore an object of the present invention to provide a method of coating metal surfaces immersed in oil-based lubricants with a friction-reducing and wear-reducing film that has improved durability.
It is another object of the present invention to provide a method of coating metal surfaces immersed in oil-based lubricants with a durable friction-reducing and wear-reducing film electrochemically by pretreating the metal surface with a molybdenum film and bombarding the surface with inert gas ions.